Field of the Invention
The present invention relates to a method for determining an operational readiness state of an electric motor, preferably a pump motor for pumping an operating fluid, for example, an aqueous urea solution, in a vehicle.
Description of the Related Art
Such a method is known from document WO 2009/147146 A1. In this known method the operational readiness state of an electric motor configured as a pump motor for pumping aqueous urea solution is determined based on the temperature of the aqueous urea solution to be pumped. If this temperature lies above a prescribed temperature threshold value, it is determined that the electric motor is ready for operation and that a pumping operation can be started. On the other hand, if this temperature lies below the temperature threshold value, it is determined that the electric motor must be heated in order to transfer it into an operational readiness state.
In the method known from this document, indirect determination of the operational readiness state of the electric motor based on the temperature of the aqueous urea solution to be pumped is disadvantageous, since the temperature of the aqueous urea solution need not necessarily be identical to the temperature of the electric motor. The temperature of the electric motor can be lower than the temperature of the aqueous urea solution so that in the extreme case frozen aqueous urea solution can be on the electric motor, while the temperature at the location of the temperature sensor lies above the temperature threshold value. In such a case the state of the electric motor would be determined as ready for operation, so that under certain circumstances with actual starting of a pumping operation the electric motor could be damaged.